In the late '60s Sydney Lewis Jr. shoplifted; now he hires guards to protect his chain of stores from nimble-fingered thieves.

Once a long-haired college radical, Lewis decried the capitalist system. Today, his hair short, he sits in a suit behind a desk computing sales figures, the tape from his adding machine curling down to the carpet.

Though he was the oldest son in a wealthy Richmond family (his father is a well-known philanthropist and businessman who began Best & Co.), the younger Lewis lived for 18 months in a modest trailer, traveling around the country. He and his father didn't speak; now they do.

Today, almost in spite of himself, Sydney Lewis Jr. is getting rich.

A former graduate student in economics at MIT (his undergraduate degree in math came from Washington and Lee), Lewis hurled abuses at the establishment in the late '60s and early '70s. In 1972 he arrived in Washington to help a friend dabble in real estate in the Adams-Morgan neighborhood. Eventually he bought a big building that housed a furniture store and opened a drug paraphernalia and clothing store.

"What happened was my business grew and grew, and I had to start dealing in credit and all of a sudden I was in the middle of it. I had no choice," says Lewis. "I started working 18 hours a day, but I didn't know it was going to be a prison . . ."

It's a profitable prison, a chain of five outlets called The General Store. When Lewis saw how well jeans sold, he dropped the dope-smoking implements and concentrated on selling clothes at discount. He cut overhead by locating in low-rent neighorhoods and by eschewing the decorations and frills that cost other stores money. In 1978 his stores sold about 400,000 basic Lee and Levi's jeans at $9.98 each.

"We more than doubled our volumn each year for the last three years," Lewis says. He pays himself $25,000 out of profits and plows the rest back into his mini-empire of five stores. "We believe Washington can handle 11 stores, and we like Philadelphia as a second city.

"A lot of people want to see me as a radical, a do-gooder. But selling jeans was just a wedge into the market; it's my gimmick. I said when I was 35 I was going to buy a camper and hightail it out of here. I've only got 11 months left, and I don't see that as a feasible situation."

But Lewis (he recently married a blues singer who once worked in his stores) figures if his adding machine is correct, it'll only take five more years before he can "let the business run without me so I can look for something else to do."